Great Barrier Reef is in the cyclone zone. The strength and duration of the storm can cause varying levels of damage to the coral and the local ecosystem plus the animals that inhabit the ecosystem. Strong winds and low pressure systems can create strong destructives waves that cause damage to the coral themselves. In March 2006, Dunk Island, a small continental island 4km of the North Queensland coast was battered by Cyclone Larry. The island was decimated however much of the unseen damage occurred to the coral around the island, the levels of coral bleaching were significant after the storm. “Cyclone Larry passed to the north of Dunk Island resulting in an 81% reduction in coral cover at 2 m depth on the northern side of the island, while at the same depth on the southern side, only 2% of the coral cover was lost.”
Sediment can also be carried and deposited by waves causing the coral ecosystem to be buried in a particular area. If there is heavy rainfall during any given time, this will alter the level of salinity in the water cause changes that can be detrimental to the livelihood of these corals. The turbidity of the water can also be increased due to the fact that the precipitation has a mixture of many oxides and chemicals in the air that have condensed into single droplets. The turbidity can affect the sunlight penetration into the water and can hinder the growth of the coral as the sunlight is vital for their survival and for the crucial process of photosynthesis. If they are starved of this sunlight then they may die. The excess rainfall can also alter the temperature level of the sea water and it could be disastrous for the coral if it were to leave the temperature range of 25-29 degrees Celsius in which the corals flourish.
The most favourable conditions for coral reef growth are those with high wave energy. Reefs act as a barrier against waves and they absorb most of their energy. This causes the waves to be weaker once they have passed through them creating much calmer waters. The water flows in the Great Barrier Reef are the driving force behind the great diversity that exists there. For the majority of the year the cooler currents from the south move into the tropics and flow into the reef. In contrast, the summer months see a change with warm water from the north bringing high levels of nutrients to the ecosystems and causing the salinity in the water to fluctuate at that time of year. The ecology of the reef depends on this natural cycle as the ecosystem has adapted to this pattern over a long course of time.
Coral polyps are the skeletal remains of coral once they have died. These undergo a natural process and form limestone. Through fluvial processes this limestone is first weathered and is deposited around the coral ecosystem. This build-up of sediment can cause the formation of coral cays. These are low lying islands that have been made from the remains of coral over thousands of years. The accumulation of limestone creates underwater landforms on which new coral can grow. This is extremely helpful in the functioning of their ecosystems as they will be more resilient to damage from waves as they will have a solid natural structure to protect them. The flow of sediment both from waves and from runoff of the land can affect coral reefs. In the Great Barrier Reef fringing reefs are found in the areas around continental islands, which are prominent throughout the whole region. These are located in close proximity to the shoreline. Due to the nature of the weather nearby, considerable rainfall causes these corals to be buried and they will ultimately die.
The Great Barrier reefs contains a colossal amount of diversity. “The reef is the largest World Heritage site in the worldâ€¦.and it has around 360 species of hard coral” (direct quotes from textbook). The Great Barrier Reef consists of a northern and southern region, with the northern region having the greater amount of diversity, much of which does not or cannot function in the southern region.
Small creatures known as polyps are responsible for creating reefs. Polyps have a symbiotic relationship with zooxanthellae, algae that lives within it. The polyp undergoes the process of photosynthesis whereby it produces necessary nutrients for its survival while the zooxanthellae produce oxygen and sugars. Eventually polyps grow and reproduce, this process continues until a reef is formed with millions of small polyps. Due to the high diversity that exists within coral reefs there is always dead matter that it releasing nutrients into the water allowing all the life there to thrive. Parrotfish are a species of fish that benefit from coral reefs. (See Appendix A, figure 1.1). These multi-coloured fish live in reefs and eat algae filled polyps which account for the majority of their diet. Cnidarians, echinoderms and crustaceans are also other vital organisms that contribute to the functioning and diversity of reef ecosystems.
Cnidarians are animals that do not have a backbone. Some cnidarians can’t move such as coral which others can such as jellyfish. The word echinoderm means ‘spiny skin’. These organisms are complex as their bodies are usually consisting of a few parts. Some prime examples of echinoderms are sea urchins and starfish. There are also many types of crustacean that inhabit reef ecosystems. They include prawns, reef crabs and reef lobsters. These crustaceans are sea floor dwellers and they tend to eat dead matter that reaches the sea floor. This may include dead fish or other organisms that die in the reef. Along with these small creatures larger mammals include sharks, whales, turtles, sea snakes molluscs and dolphins. Dugongs are also found in coral reef ecosystems. With some of the world’s largest concentration of dugongs calling Australia’s Great Barrier Reef home.
There are three key factors that affect the way sand dunes function in the atmosphere. They are wind, precipitation and temperature. Aeolian transport refers to the movement of sand by wind. The factors that determine the amount of sands that is transported are; the type of vegetation in the area, the size of the sand particles, the topography in which the sand was located and the size of the sand particles. Stronger winds pick up more sand than calmer winds and this increases the amount of sand that gets deposited in different compartments along the coast. The prevailing wind can also affect how sand is moved around. In areas of high vegetation, Aeolian transport is difficult as the roots of the plants bind the sand, making it harder to dislodge. They also act as barrier absorbing most of the power of the wind.
Precipitation determines the type of vegetation that lives in the area in which the sand dune has formed. If a coastal area is very moist with constant rainfall then it will have considerable vegetation to bind the sand together, however if it has a dry climate there will be a lack of vegetation thus meaning that there will be a less diverse range of vegetation, sand will not be bonded strongly by plant roots resulting in an unstable ecosystem that can suffer from change easily.
Temperature plays a key role in affecting the rate at which the sand dries. In areas of warmer weather sand will dry faster, thus allowing the wind, through Aeolian transport to deposit sand further up the beach and form a foredune. In stark contrast cooler weather will leave the sand wet for longer periods of time resulting in less deposition of sand and smaller dunes, leaving the land prone to erosion from the wind and sea water. Temperature also affects the types of vegetation that grow in coastal areas. Having considerable sand dunes works in favour of vegetation growth, as more diverse pioneer grasses such as spinifex, pigsface, and goatsfoot and guinea flower can grow allowing the sand to have a stronger bonding from their roots. Temperature can also have an impact on ocean currents. The sun can cause convection currents in the ocean which allows water of different temperatures to move, albeit at very low speeds however changes in water flow can also affect the distribution of sediment on beaches and ultimately coastal dunes.
Hydrological processes are the main reason for the formation of sand dunes. Water erodes cliffs and headlands through fluvial processes such as abrasion and hydraulic pressure causing sediment as a result. More often than not these sediments make their way into sediment compartments such as bays. Sediment that does not directly enter bays accumulates in offshore deposits on landforms such as sandbars. Sandbars play an important role in regulating the amount of sediment reaching the coast as waves hit them and deposit the sediment closer to the land. The process of longshore drift is also instrumental in the formation of sand dunes. Longshore drift refers to the movement of sediment parallel to a beach. Longshore drift fosters the growth of coastal dune systems as they can form far away from where the sediment deposit is. With an excess of sand in one area sand will eventually be deposited further up the beach causing the creation of dunes and a foredune.
Waves also affect the way that coastal dunes form. Destructive waves such as plunging waves can remove sediment from a beach resulting in a smaller dune over team which results in a loss of habitat and biodiversity. These waves mostly occur during storms when large amounts of sediment can be lost in a short period of time. Constructive waves such as surging and spilling waves increase the amount of sediment on beaches hence increasing the size of the dune and foredune as well as the amount of biodiversity in the coastal dune system. Considerable rainfall can cause runoff that eventually reaches the coast, due to the fact that it is a low lying area. Water will infiltrate the dunes causing the water table to rise, meaning that the dune will be saturated. When the sand dune dries the water table decreases however much of the vegetation on the dune has either drowned or has been washed away. Now that the sand is not bound together by the vegetation, it is exposed to erosion by water and by wind.
The accumulation of sediment over time has led to the creation of coastal dune systems. These systems are dynamic, they are constantly changing. The main sources of sediment for sand dunes are offshore sandbar deposits and sediment that had also accumulated at the mouth of narrow rivers. These sediments reach the coast through the process of longshore drift. Along with this is the action of the waves which forces sediment up onto the swash zone and eventually onto the berm until it accrues to form a dune or foredune. There are three main types of dunes are parabolic dunes, foredunes and parallel dunes.
A parabolic dune is a sand dune that is in the shape of a U or V. these dunes can be very long and they form parallel to the coast. Parabolic dunes form where strong winds hit the coast, allowing for the dune to become larger and to retreat inland. Parabolic dunes move backwards in the direction of the prevailing wind. The strong winds that move landward create an axis in the dune, allowing it to grow. The sides of the parabolic dune are called its arms; they frequently have vegetation growing on them which contributes to the stabilisation of the dune. A lack of vegetation on the arms of the dune will cause instability. The entire dune may collapse causing Aeolian transport to move the loose sand (sediment) somewhere else along the beach or to a parallel dune.
A foredune is an accumulation of sand at the back of a beach. Over time sand accumulates in the swash zone, dries up and it is moved landward via Aeolian transport. Subsequently this sand amasses in the berm and eventually forms a foredune which can protect the land from further erosion.
Parallel dunes form when several foredunes are aligned at a right angle to the beach face. When a foredune is affected by a large storm, destructive waves take away most of its sand. This leaves the foredune unstable. Eventually, constructive waves will bring sediment back to the beach however; the accumulation of sand will begin to occur in front of the original foredune. While a new foredune begins to form, the original foredune is shielded from waves and the prevailing wind and therefore it becomes stable as more vegetation begins to grow on it. This process has occurred in many coastal areas around Australia resulting in many foredunes forming on a beach that are parallel to each other. Eventually the foredunes furthest back on a beach are completely vegetated and stable and are consequently difficult to destabilise.
Coastal dunes support a variety of complex and diverse plant and animal species. While newer coastal dunes tend to have more pioneer grasses, older dunes are more stable as they support a much more diverse set of plants due to their well-developed soils. Coastal dunes have a variety of species divided into three groups. Primary, secondary and tertiary species. Primary species usually occupy the pioneer zone; this is the area between the top of the beach and the foredune. The sand in this area contains considerable salinity as it is constantly subject to sea spray. Therefore the plants that grow here are highly specialised as they are acclimatised to these conditions. Beach Spinifex or Spinifex longifolius is one of the most abundant species in coastal dunes and it is commonly found in this zone (See Appendix A figure 1.2). Beach spinifex has been used to stabilise dunes across Australia’s coast which it has done successfully along with pigface which can flourish in such conditions due to its resilience to the salt content in the sea water. Examples of secondary species are coastal Banksia, coastal wattles and she-oaks. These are found on stable foredunes. Coastal wattle and coastal banksia predominantly grow on less developed yet stable foredunes whereas she-oaks due to their large size would grow further back on the beach on an extremely developed and stable parallel dune. At the back of a beach lie the most stable dunes. These dunes are characterised by larger vegetation such as a trees. These dunes were originally foredunes themselves and over time parallel dunes may have formed in front of them protecting them from the spray and erosive power of the waves. The nature of species that exist here will depend on the climate of the area. A more moist climate will support more diverse life however a dry climate may mean that a smaller diversity of species inhabit the area. Due to the fact that tertiary species live further landward there will be more organic matter present and the sand will almost be soil like. Paperbark trees also known as Melaleuca are prominent in this region and they may even develop in swales, providing that there are well developed soils. Paperbark trees are found at the back of coastal dunes systems and are given the title of climax communities as they are said to have a balance with their environment due to the fact that they are fully developed and acclimatised to their ecosystem.
Atmosphere: Natural and human impacts on Coral Reefs
Natural stress and human induced modifications have a profound impact on coral reef ecosystems. Pollution plays a large role in shaping the way coral reefs function. Harmful greenhouse gasses accumulate and rise into the troposphere affecting the air that all organisms absorb. Harmful chemicals from the burning of fossil fuels and car exhausts cause this process as they can stay in the atmosphere for up to 70 years. Another culmination of this is photochemical smog. After evaporating and eventually condensing the chemicals mixed with dust particles and water vapour fall as precipitation on the Earth’s oceans and on coral reefs. Acid rain in large amounts can pollute water and cause turbidity levels to rise. The turbidity increases the cloudiness of the water and reduces the sunlight that corals need for their growth. With the lack of sunlight, coral bleaching occurs and coral ecosystems may die out which can affect their other organisms that rely on them as a source of food or as a breeding ground. Examples; Parrot fish. These consequences also occur when there is an increase in phosphate and nitrate due to precipitation. These chemicals encourage algal growth on coral, also causing coral bleaching due to the lack of sunlight.Climate change can occur either naturally or through human induced changes around the world. This can cause a microclimate to form, hence directly impacting the ecosystem. Human induced climate change may occur due to the use of chlorofluorocarbons. These organic compounds are found in aerosol cans and cause ozone depletion because the accumulation of CFC’s in the atmosphere chemically react with the ozone thus destroying it. This subjects the earth to an increase in sunlight exposure and ultraviolet radiation which can bring about an increase in temperature. Coral ecosystems are sensitive to a temperature change and can die as a result of this. Similarly if too much pollution is prevalent in an adjacent urban area, pollutants in the atmosphere can hinder sunlight, consequently causing a drop in water temperature which will have similar effects on the coral and their interdependent organisms as with an increase in water temperature. Natural disasters such as cyclones and tsunamis also cause extensive damage to coral ecosystems. Underwater earthquakes can cause an entire seabed to collapse meaning that life there can no longer be sustained.
Hydropshere: Natural and human impacts on Coral Reefs
Coral reefs are also affected by the hydrosphere. Precipitation on land can come back as runoff into the ocean or through waterways that eventually drain into the ocean. Along the way sediment may have been picked up and will eventually be deposited in the water, polluting it, raising turbidity and killing coral. This natural change can be detrimental however some sediment that is deposited in the coral ecosystem may be from humans. Examples may be plastic bags, bottles even wrappings for food. Infiltration and percolation also bring ground water to the sea along with many chemicals that have leached into the soils. These chemicals change the composition of the sea water promoting the growth of toxic algal blooms and ultimately killing coral and other sea life. This is another example of how a natural process combines with human activity to cause further damage to coral ecosystems.
Chemicals from humans can also come in the form of tourism. Australia’s Great Barrier Reef is a world class tourism destination that attracts thousands of tourists every year due to its natural beauty. One of the main highlights for any tourist is to dive underwater to witness the diversity of life that exists. This can result in people touching corals or removing them from their natural habitat and as a result killing them. Glass bottom boats or normal charter boats that visit the reef may have their anchors trailing below them. This can have a devastating effect on the reef because metal anchors can scrape through corals, and destroy them. A recent report by the Great Barrier Reef Marine Park Authority states that over 2,000 ships travel through the Great Barrier Reef every year and fears have grown amid news that states near collisions with coral reefs have not been reported. This was further backed up by an anonymous interview carried out on 82 ship captains who claimed that had near groundings on the reef. Although no groundings have occurred, the Marine Park Authority believes that the likelihood of a major spillage is around 93% within the next 20 years. A spill of this extent could spread over many kilometres and eventually oil would form a thick black coating on coral and other marine organisms that interact with the coral. The high toxic levels in the water would kill both marine plants and animals and interrupt the breeding that would occur in the coral ecosystem. An event such as this could occur over a matter of hours or days and marine life in the vicinity of the spill would not adjust to the change.
Lithosphere: Natural and human impacts on Coral Reefs
Natural processes play a predominant role in how Lithospheric components impact on coral reefs. Waves constantly which away at large masses of rock (fluvial process). This breaks down and waves eventually carry the sediment creating turbid waters which can kill corals in the short term. However, the International Coral Reef Symposium compiled a report in 2000 suggesting that “the waters at many coral assemblages in the ‘coastal turbid-zone’ along the GBR coastline have probably been naturally turbid for millennia”. As a result of these findings it can be concluded that the coral of the Great Barrier Reef have adjusted to the turbid waters. These findings suggest that natural stress that occurs over a long time is much easier to adjust to; this is why the corals there are able to survive with a smaller amount of sunlight, a sudden change in sediment would exacerbate the turbidity level in the water and could disturb dynamic equilibrium causing the coral to be affected . Weathering and erosion causes sediments to be freed up and makes them easily movable. Topography affects the extent to which the land can be eroded. This depends on whether the land is fertile, well mulched, strongly bonded or dry. Arid land is much weaker and has larger sediment discharge.
Biosphere: Natural and human impacts on Coral Reefs
Natural and human impacts on Coastal Dunes
Natural changes such as wind, temperature and precipitation affect coastal dunes. Wind through Aeolian transport affects the movement of sand along a beach and aids with the formation of dunes. Precipitation affects the nature of vegetation that grows on the sand dunes, which ultimately affects the strength of the dune system. Temperature affects how dry the sand dune is and how long it remains wet after being affected by waves. Constructive and destructive winds also affect the size of coastal dune ecosystems as they determine whether sand is added or removed from there. Global warming and the rising of sea levels is another natural impact on coastal dune ecosystems. A rise in temperature on a global scale may result in higher sea levels which can decimate coastal dunes and their vegetation as well as cause erosion to the land. The introduction of exotic species has also had advantages and disadvantages. The introduction of rabbits into Australia has had disastrous consequences. Rabbits eat the vegetation on sand dunes as well as the grasses that stabilise them. This reduced the cover the vegetation provides for the sand and it exposes the sand to wind erosion meaning that whole dunes can be subject to Aeolian transport. Rabbits also live in these fragile dunes and their burrowing can cause the dune to collapse which will also result in erosion. In contrast the Bitou Bush, which was introduced from South Africa, has been successful at stabilising dunes across Australia’s east coast as it currently composes of 70% of New South Wales’ coastline. The bitou bush creates a stronger bonding in the sand and thus makes it more resilient natural and human changes. This is one of the few human induced changes that have brought benefits to coastal dunes. The bitou bush has been particularly helping as stabilising dunes after sand mining has occurred. Sand is abundant on Australia’s coastlines and sandmining on the Kurnell peninsular has changed the landscape their dramatically. The Sutherland Shire Environment Centre has said that “once towering sand dunes have been replaced by deep lakes, many of which are now being filled with demolition waste”. This is having an adverse effect on groundwater in the area. The high instance of demolition waste has disrupted the ecosystem destroying many diverse plant species and animals that would have inhabited the area (See Appendix A figure 1.3 and 1.4). Find info on the size of dunes before and after mining. Stepping on dunes by humans can also destabilise them. Similar to the impacts of rabbits, humans may trample on vital pioneering grasses and the sand dune may be subject to erosion because its natural shape has been altered.
Due to the fact that coral reefs and sand dunes are constantly being impacted on by nature and by humans the degree at which they adapt varies. It can be established that natural change takes much longer that human induced change which can be very rapid. Under these circumstances these ecosystems are more likely to adapt to natural change thus giving them a better chance of survival because their genetic makeup may be altered, however, genetic changes cannot occur in one generation but over many generations and for this reason plants and animals in coral reefs and sand dunes will struggle to survive or die out after a human induced change because they simply do not have the time to do so.
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